Basic Course: Supplemental Topics

In some locations, the nationally recommended aquatic life criteria may be considered under- or overprotective if the species at a site have different sensitivities than those included in the national criteria data set. For instance, physical and/or chemical characteristics at a site can alter the biological availability and/or toxicity of a material. For this reason, site-specific criteria may be developed to address such conditions.

Site-specific procedures consist of:

Defining the site boundaries.

Determining the effect of biological, physical, or chemical characteristics on sensitivity or bioavailability and toxicity.

Calculating numerical criteria by applying the recalculation procedure, the water-effect ratio procedure, or the resident species procedure.

Key Point. EPA regulations allow States and Tribes to develop site-specific aquatic life criteria. The Agency then considers the adequacy of the criteria during its review of the State/Tribe’s water quality standards. In general, EPA approves site-specific criteria if they are supportive of the designated uses established in the State/Tribe’s water quality standards and the criteria are based on sound scientific rationales.